Is this a mag deficiency?

[Sanspepins]

So I’m wondering if Fox Farms is organic soil? I’ve heard that it is and I’ve heard that it isn’t. If it is that would be great because I already have some ocean forest. I was thinking about just using ocean forest mixed with perlite and only big bloom throughout the entire next grow. My last grow looked good up until I started using FF Big Bloom and Tiger Bloom, everything went down hill after that.